Overview of Powerpack Testing 

done at EPA

James Sanchez

4/15/11
Driver Model

Vehicle Model

Dyno Measurement Motor Drive

Vehicle Speed

Brake Command

Torque

Speed Command

Drive Cycle

Engine

Electric Hybrid 

Transmission Dyno

J1939

ECU TCU

T

orque

Sensor

Torque

Driver & Brake Command

Speed
Mechanical Set Up

Non Hybrid System is set-up 

similarly
Test Cell Instrumentation

 GE 600 Hp DC Dynamometer

 Base Speed 2000 rpm

 2100 NM Maximum Torque Absorption

 In-Line Torque Meter (HBM)

 Test Cell Controlled Environment:

 Temperature 2 mperature 25 deg C, Relative Humidity 65% elative Humidity 65%

 Ultrasonic Flow Meter for Engine Intake Air

 Micro Motion Fuel Measurement System (AVL)

 Engine Jacket Water Cooling System

 Engine Charge Air Conditioning System

 Engine Power Supply (0-30 v or 0-50 v)

 Emissions Measurement:

 Horiba Full Flow CVS and Dilution Tunnel for Gaseous & Particulate Sampling

 A&D i-Test Software for Test Cell Automation & Data Logging


Vehicle Model Parameters

• Vehicle Mass (m)

• Coefficients of mechanical drag, 

Am, Bm, and Cm

• Final Drive Ratio

• Loaded Tire Radius (r)
Vehicle Parameters Used for Testing

Hybrid Conventional

Vehicle Mass (kg) 6450 5883

A (N) 506.12 506.12

B (N/(m/s)) 7.345 7.345

C (N/(m/s)^2) 1.960 1.960

Frontal Area (m^2) 9 9

Tire Radius (m) 0.381 0.381

Final Drive 4.1 4.1
Vehicle Model

2 F C f m m m   v B v A 

F F RL  f J F

Where:

FRL = road load force 

Ff = friction and aerodynamic drag forces

FJ = force from inertia

v = vehicle velocity

J

dv F m

dt


Torque and Speed at Transmission 

Output

r F

d

ds 2

v k

n

 r





 

Where:

nds = rotational speed of drive shaft

Tds = torque at the drive shaft

r = radius of loaded tire

kd = final drive ratio

RL

ds

d

r F T

k




Performance Criteria 

Driver Model

• ±2 mph in a 2 second window

• Actual average power has to be within ± 1.5% of scheduled average 

power

 

2

i m m i m i

i 1

N

dv v A B v C v m

dt P

N



   

      

       




Possible Criteria for

Torque Control

Parameter Torque

Slope, a 0.830 < a < 1.030

Table 2 of §1065.514—Default statistical criteria for validating duty cycles

Slope, a1 0.830 < a1 < 1.030

Absolute value of intercept, |a0| < 2.0 % of maximum mapped torque

Standard error of estimate, SEE < 10 % of maximum mapped torque

Coefficient of determination, r

2 > 0.850
Brake Model

Brake is turned off when the torque measured 

at the drive shaft is less than the torque 

defined by the road load model
Driver Model States

State Dyno/ Throttle Control

Idle 1 Torque/ Position

Launch 2 Speed/ Position

Accel/ Coasting 3 Torque/ Speed

Braking 4 Speed/ Position
Logic for Switching Between Drive 

Model States

• State1 --> State2, if velPwrtSch(+?) > 0

• State2 --> State3, if tqShaft > tqRlmVehDriveshaft(delayed)

• State3 --> State4, if posPwrtEngThrot_CAN < 1.0 and velVeh > 

(velPwrtVehSetpoint + 1) (delayed)

• State4 --> State3, if tqShaft < tqRlmVehDriveshaft(delayed)

• State2-4 --> State1, if ate1, if velVeh < 0.5 and < 0.5 and velPwrtSch velPwrtSch(+?) = 0

Where:

velPwrtSch(+?) = the cycle velocity in the future

tqShat = the torque measured at the transmission output

tqRlmVehDriveshaft = Modeled torque set point

posPwrtEngThrot_CAN = throttle position

velVeh = calculated vehicle speed from dyno speed

velPwrtVehSetpoint = the cycle velocity